1. Field of the Invention
The present invention relates generally to a method of controlling a double clutch transmission (DCT) of a vehicle and, more particularly, to a technique for preventing shift shock from occurring when shifting gears in response to deceleration of a vehicle provided with a DCT.
2. Description of the Related Art
A downshifting process of a DCT when a vehicle provided with the DCT decelerates, for example, to stop, will be described below with reference to FIG. 1.
When the vehicle decelerates, a transmission controller generates an order to shift gears from a preceding gear N+1 to a current gear N set as a target gear. Thereafter, the transmission controller releases a clutch which has been in an engaged state at a preceding gear N+1, and then releases a clutch of a corresponding input shaft, before releasing the preceding gear N+1 so that the corresponding input shaft enters a freely rotating state.
Subsequently, when shifting to a subsequent gear N−1, the clutch of the input shaft is temporarily engaged to make the rpm of the input shaft which higher than that of the output shaft before the shift gear of the subsequent gear N−1 is engaged. Thereafter, a shift gear of the subsequent gear N−1 is engaged. Thereby, shift shock can be prevented from occurring.
In other words, if the rpm of the input shaft is less than that of the output shaft when engaging the shift gear of the subsequent gear N−1, backlash of elements pertaining to transmission of power between the input shaft and the output shaft, which has been arranged in one direction when synchronization takes place for engagement of the shift gear of the subsequent gear N−1, is rearranged in the reverse direction when the synchronization is completed or the transmission of power from the input shaft to the output shaft begins. At this time, shift shock and noise occur. To avoid such a phenomenon, as stated above, the technique of FIG. 1 is configured such that the clutch is temporarily engaged before the gear engagement of the subsequent gear N−1.
However, while gears are shifted from the preceding gear N+1 to the subsequent gear N−1, a series of frequent movements of the clutch in which it is released, engaged and released again, may cause another kind of abnormal shock and noise. Moreover, the frequent movement of the clutch is responsible for the durability of the clutch and an actuator of the clutch deteriorating.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.